Terrain glitch

A terrain glitch is a terrain bug where the terrain generator makes a mistake when generating this part of celestial body's surface.

Polar Glitch

This is the most usual type of terrain glitch. It occurs as a very strange terrain on the poles of celestial bodies, like Moho or Eve. It's most likely a mistake happening when terrain generator attaches height values to a sphere.

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  A probe wedged in the 5km-deep "well" at north pole of Moho.

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  Terrain at Eve's south pole

Terrain Breakage

As is shown in its name, this is a glitch that terrain cracks. It provides an "entrance" to the "inner" of a celestial body, but unfortunately, when flying something(like a poor Kerbal) into the crack, it will be destroyed immediately as it's under the surface.

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  A glitch near 23.39N, 187.80W on Minmus.